Protozoan parasites of the genus Leishmania are the causative agents for a group of serious diseases (known as Leishmaniasis) infecting 10-12 million people worldwide. Current drugs for leishmaniasis are plagued with low efficacy and high toxicity. With resistance on the rise and no safe vaccine available, there is an urgent need to maintain a steady stream of new drugs and potential drug targets. The PI's long term goal is to decipher the molecular strategy utilized by Leishmania parasites to thrive in sandflies and mammals. Advancement in the fundamental mechanism of pathogenesis can lead to new and improved treatments. In mammalian cells, sphingoid bases (SBs) and their phosphorylated derivatives are powerful signaling molecules regulating a plethora of essential pathways. Recent studies demonstrate that Leishmania parasites possess a very active SB metabolism with important yet poorly defined functions. The objective of this application is to elucidate the vital roles of SB metabolism in Leishmania proliferation and virulence. Formulated on the basis of strong preliminary studies, the central hypothesis is that SB metabolism is required for the adaptation of Leishmania parasites to the harsh environment in mammals, the removal of toxic metabolites, and the synthesis of essential phospholipids. Rationale for the proposed research is that a better understanding of this critically important and somewhat dangerous pathway will provide novel insight into parasite-host interaction and uncover new clues to control leishmaniasis. Two specific aims will be undertaken to test the central hypothesis: aim 1 is to elucidate the crucial roles of sphingosine kinase (a key enzyme in SB metabolism) in Leishmania; and aim 2 is to determine why Leishmania needs ethanolamine phosphate (an intermediate in SB metabolism) to survive. Each aim will explore one branch of the SB metabolic pathway in Leishmania. Genetic knockout mutants and their complemented controls will be generated and characterized using molecular, cellular, and biochemical approaches. Successful completion of these studies will significantly improve our understanding of SB metabolism in Leishmania and the function of lipid metabolites in general. This project is highly significant because in addition to the exciting new knowledge, a number of novel drug targets may emerge at the conclusion of these studies.